An internal combustion engine burns fuel inside a confined space called a combustion chamber. This exothermic reaction of a fuel with an oxidizer creates gases of high temperature and pressure, which are permitted to expand. An internal combustion engine allows the expanding hot gases to work directly on a piston, moving the piston. An internal combustion engine can be contrasted with an external combustion engine. An external combustion engine, such as a steam engine, uses combustion to heat a separate working fluid, such as water or steam. The working fluid then performs work on the piston.
The most common type of internal combustion engine is a reciprocating engine, such as a two-stroke, four-stroke, or diesel engine. The first practical four-stroke engine was developed by Nikolaus Otto working with Gottlieb Daimler and Wilhelm Maybach in 1876. The first practical two-stroke engine was developed three years later by Karl Benz. The reciprocating internal combustion engine has come to dominate the ground transportation, such as cars and trucks.
In a reciprocating internal combustion engine, the combustion is intermittent, rather than continuous. The reciprocating internal combustion engine converts its reciprocating motion into rotational motion using a crankshaft that is connected to the pistons with a plurality of connecting rods. Typically, to get the rotational motion to the drive shaft, it goes through a transmission.
Reciprocating internal combustion engines lose significant amounts of energy, and therefore efficiency, through frictional losses. The crankshaft and connecting rod assemblies are complex and add significantly to the frictional losses, size of the engine, and weight of the engine. In applications that are using rotational energy to produce electricity, reciprocating internal combustion engines are inefficient, although sometimes utilized for lack of reasonable alternatives. Reciprocating internal combustion engines are also difficult to package in many applications, due to their size and weight.
There is a market for a small internal combustion engine that is lighter, simpler, and more efficient than traditional two-stroke and four-stroke engines. In fact, there is a good argument that the lack of such an engine inhibits certain markets such as portable power tools and drones. Such a lightweight, simple, and efficient internal combustion engine would have to solve the problem of translating reciprocal motion into rotational motion in a more efficient manner.